1. Field of the Invention
This invention relates generally to an integrated circuit including a substrate having part-way through vias and, more particularly, to an integrated circuit including a dense configuration of integrated circuit components formed on a top-side of a substrate and plurality of part-way through vias formed through a back side of the substrate and opposite to the circuit components, where the part-way through vias operate to suppress substrate modes.
2. Discussion of the Related Art
Integrated circuits are typically fabricated by epitaxial fabrication processes that deposit various semiconductor layers on a semiconductor substrate to define the circuit components. As integrated circuit fabrication techniques advance and become more complex, more circuit components are able to be fabricated on the substrate within the same area and be more closely spaced together. Further, these integrated circuit fabrication techniques allow the operating frequencies of the circuit to increase to very high frequencies, well into the GHz range.
Substrates for integrated circuits are made of various semiconductor materials, such as silicon, InP, GaAs, etc., that promote substrate signal propagation modes that allow the RF signals used by the circuit to propagate through the substrate. Particularly, high refractive index epitaxial layers can act as parasitic waveguides and allow signal propagation. These substrate signal propagation modes can significantly attenuate certain frequencies, such as frequencies in the 550-1000 GHz range, and cause severe signal losses. Because the substrate modes attenuate the signal propagation, it may be necessary to increase the power required to transmit the signals through the circuit, which has power limitation drawbacks.
Signal propagation modes in the substrate can be reduced, or eliminated, by decreasing the thickness of the substrate, where the reduction of the thickness of the substrate would be inversely proportional to the operating frequency of the circuit to be effective. A thinner substrate reduces the area through which the substrate modes can propagate. However, fabrication techniques limit how thin the substrate can be, where the fabrication limits of the substrate thickness is typically reached before the fabrication limit of the circuit operating frequency.
One way to overcome signal propagation modes in the substrate is to provide more metal vias extending through the substrate that act to suppress the substrate modes. Particularly, by placing conductive elements in the path of the signal propagation modes, the modes are broken up, which reduces their ability to allow propagation of the signal. As the frequency of the circuit goes up, the number of vias that are required to suppress the substrate modes goes up proportionally, assuming that the thickness of the substrate remains constant. For example, when doubling the operating frequency of the circuit, the number of vias also needs to be doubled. Further, as the frequency of the circuit goes up, the density of the components required to operate at that frequency also goes up. However, the density of the circuit components fabricated on the top-side of the substrate limits the number of vias that can be formed through the substrate without inferring with the components.